1. Technical Field
The present invention relates to a droplet discharging head, a droplet discharging apparatus, a method for manufacturing a droplet discharging head and a method for manufacturing a droplet discharging apparatus.
2. Related Art
For example, an inkjet head mounted in an inkjet recording apparatus is known as a droplet discharging head for discharging droplets. The inkjet head generally includes a nozzle substrate in which a plurality of nozzle holes for discharging ink drops are formed, a discharge chamber which is joined to the nozzle substrate and which communicates with the nozzle substrate through the nozzle holes, and a cavity substrate in which an ink flow path such as a reservoir is formed. The inkjet head is structured such that ink drops are discharged by pressure being applied by a drive section to the discharge chamber. Drive means includes a type of utilizing electrostatic force, a piezoelectric type using a piezoelectric element, and type of utilizing a heating element.
Among inkjet heads as described above, there is a demand for an inkjet head with a structure having a plurality of nozzle arrays to achieve high-speed printing and color printing. Furthermore, along with recent increase in nozzle density and increase in length of the ink jet (i.e., the number of nozzles per array), the number of actuators in the inkjet head has been more and more increased.
A reservoir which is common to the discharge chambers and which communicates with individual discharge chambers is provided in the inkjet head. Accordingly with an increase in nozzle density pressure of a discharge chambers is transmitted also to the reservoir, and thus the pressure also affects other discharge chambers and the nozzle holes which communicate with the other discharge chambers. For example, when positive pressure is applied to the reservoir by driving of the actuator, ink drops leak from non-driven nozzles which are not the nozzle holes (i.e., driven nozzles) through which the ink drops should be discharged. On the other hand, when negative pressure is applied to the reservoir, the amount of ink drops which should be discharged from the driven nozzles decreases. As a result, printing quality is deteriorated.
To prevent pressure interference between the nozzles as described above, there have been disclosed arts of assembling a unit referred to as an ink distribution plate having a diaphragm section to a member in which the nozzles are formed. (For example, refer to FIGS. 1 and 2 in Page 1, JP-B-2-59769.)
However, in the art disclosed in JP-B-2-59769, the ink distribution plate is separately assembled in the member in which the nozzles are formed, and therefore it is difficult to reduce the size and thickness of the inkjet head.
To overcome this disadvantage, inkjet heads have been disclosed in which a diaphragm section for buffering pressure fluctuation in the reservoir is provided in the nozzle substrate. (For example, see FIGS. 1 and 2 in Page 2, JP-A-11-115179).
In the inkjet head disclosed in JP-A-11-115179, however, since the reservoir and the discharge chamber are formed in the same substrate (the cavity substrate), it is difficult to provide a diaphragm section and the reservoir in the same substrate from the viewpoint of securing the volume of the reservoir. Accordingly this structure causes a section with insufficient strength to be exposed to the outside despite the fact that the diaphragm section is formed in the nozzle substrate. Therefore, there is a limit in reducing the thickness of the diaphragm section, and a protective cover or the like is separately needed.